Stainless Wire and Rope Stretch Characteristics - Modulus of Elasticity - Break Load

Stretch is a characteristic of all wire ropes; constructional stretch initially (as the individual wires 'bed down') and then as conventional elastic stretch.

This permanent stretch can be as much as 0.1% for a 1x19 strand.

Once a cable has bedded down it will obey Hookes Law; elastic stretch will be proportional to the load applied. Resistance to this stretch is determined by the modulus of elasticity.

Where stretch is critical to the application, constructional stretch can be eliminated by pre-tensioning or pre-stressing. This can be carried out during manufacture or swaging.

Pre-stressing is usually only applicable on large bridge structures and is not necessarily appropriate on structures where rigging screws and tensioning devices are used to take up any stretch.

Elastic stretch can be calculated by the following formula:

Elastic Stretch = (W x L) / (E x A)

W = Applied Load ( kN )
L = Cable length ( mm )
E = Strand Modulus ( kN/mm2)
A = Area of Cable = (D2 x pi) / 4 (where D= Dia of cable mm)

Typical values for E are:
1x19 = 107.5 kN / mm 2
7x7 = 57.3 kN / mm 2
7x19 = 47.5 kN / mm 2
Dyform = 133.7 kN / mm2

The graph shows typical breaking loads for our hardware compared against conventional 1x19 and Dyform 316 stainless steel cables.

It should be noted that stainless steel wire rope and strand will start to distort at around 50% of its breaking load. It is therefore advisable not to load cables to more than 50% of their breaking loads.

Factors of safety should always be applied when calculating maximum loading conditions. In cases of doubt, an engineer should be consulted to assess the loading and advise on suitable factors of safety to ensure that overloading cannot occur.

To convert kN to KgF divide by 0.009807. To convert kN to LbF divide by 0.004448.